Lips are the soft, fleshy structures that form the opening of the mouth in humans and many animals. They are composed of skin, muscle, and mucous membranes, allowing for movement and flexibility. Lips play a crucial role in various functions, including eating, speaking, and expressing emotions. The outer layer of the lips is typically more pigmented than the surrounding skin, giving them their distinct color. The upper lip and lower lip can vary in size and shape among individuals, contributing to unique facial features. Lips are also sensitive, containing many nerve endings that enhance the sense of touch.